Method of delustering acrylic fibers

ABSTRACT

DELUSTERING POLYACRYLONITRILE FIBERS BY DISPERSING A PARTICULATE DELUSTANT IN A SOLUTION OF A CELLULOSE ESTER, INCORPORATING THE DELUSTRANT DISPERSION INTO POLYACRYLONITRILE SPINNING SOLUTION AND STABILIZING THE SPINNING SOLUTION MIXTURE AGAINST FLOCCULATION.

United States Patent "ice 3,746,672 METHOD OF DELUSTERING ACRYLIC FIBERS Darrell R. Thompson, Somerville, N.J., assignor to Celanese Corporation, New York, NY.

No Drawing. Filed Mar. 30, 1971, Ser. No. 129,626 Int. Cl. C08f 29/54 US. Cl. 260-17 R 8 Claims ABSTRACT OF THE DISCLOSURE Delustering polyacrylonitrile fibers by dispersing a particulate delustrant in a solution of a cellulose ester, incorporating the delustrant dispersion into polyacrylonitrile spinning solution and stabilizing the spinning solution mixture against flocculation.

The present invention relates to a method for producing delustered high acrylonitrile polymer fibers. More particularly, it relates to a method for the uniform dispersion of a finely divided particulate delustrant throughout solutions used in spinning fibers from high acrylonitrile polymers, with minimal aggregation, i.e. clumping, flocculation, agglomeration, and the like, of the delustrant particles.

It is well known that polyacrylonitrile and copolymers of acrylonitrile with at least one other ethylenically unsaturated compound are excellent fiber-forming polymers. The polyacrylonitrile and polymers of more than 85 percent acrylonitrile and up to about 15 percent of other ethylenically unsaturated compounds produce fibers with superior tensile properties, desirable elongation and excellent stability under a wide range of physical and chemical conditions. However, these fibers, as spun, have a high sheen or luster which is a serious disadvantage for many fiber end uses.

-It is necessary to produce delustered fibers for many textile end uses. Many of the synthetic organic polymeric fibers are characterized by a high surface sheen when spun in a conventional manner. This surface sheen or luster may be eliminated or diminished by the addition of melt additives, surface finishes and the like to modify the light reflectance characteristics of the surface of the fiber.

The more luxurious natural fibers, particularly Wool, exhibit a very low sheen or luster. When a synthetic fiber is to be used for such end uses as dresses, carpets, mens suits, and the like, which are substantial outlets for W001 yarns, it is necessary to modify the surface characteristics of the fibers to reduce their sheen to produce a fiber which resembles the natural fibers in appearance. A product having a glossy, shiny surface will most often be considered inferior in the marketplace when compared to the dull appearing wool product. Acrylic fibers are often utilized as wool substitutes and, therefore, must be compatible with wool in appearance.

Generally, it is a relatively simple operation to incorporate a finely divided delustrant into a fiber-forming synthetic organic polymer spinning solution. Normally, with an acrylonitrile polymer spinning solution, one of the components of the spinning solution acts as a carrier for the particulate delustrant. The delustrant is added and thereafter mechanically dispersed throughout the spinning solution, preparatory to extrusion.

There are certain circumstances when it becomes impracticable to incorporate delustrant into acrylonitrile fibers in the conventional manner. This is especially true for fiber-forming acrylonitrile polymer solution wherein during spinning the spinning solution is maintained under superatmospheric pressure and at a temperature above the atmospheric boiling point of the solvent. In such 3,746,672 Patented July 17, 1973 a system the delustrant must be dispersed in a fluid medium before injection into the spinning system to avoid clustering or flocculation of the particulate delustrant. The present process is particularly applicable to acrylonitrile polymers in low boiling solvents, such as acetonitrile or acetonitrile and up to about 40 weight percent water, the solutions of which solidify at temperatures below. the atmospheric boiling point and/or upon the release of the imposed superatmospheric pressure.

[It is an object of the present invention to provide spinning solutions of polymers containing at least percent acrylonitrile having dispersible delustrants sub stantially uniformly distributed throughout. It is another object of the present invention to provide a method for spinning delustered acrylic fibers wherein during spinning the spinning solution is maintained under superatmospheric pressure and at a temperature above the atmospheric boiling point of the solvent. These and other objects will be apparent to those skilled in the art from the description of the invention which follows.

These objects are accomplished according to the present invention by dispersing a particulate delustrant such as a colored pigment or pigmentary TiO preferably of a particle size of less than about 10 microns, most preferably less than 5 microns, by ball milling or other suitable grinding technique in a solution of cellulose ester, preferably a fiber-forming ester such as cellulose triacetate or cellulose acetate. The cellulose ester solution comprises from about 2 percent to 20 percent by weight cellulose ester in a solvent which is a non-solvent for high acrylonitrile polymers, e.g. acetone. The dispersion of the delustrant or pigment in the cellulose ester solu tion comprises from about 15 to 45 percent, preferably from about 25 to 35 percent, by weight particulate delustrant; from about 1 to 17 percent, preferably from about 3 to 15 percent, by weight cellulose ester; and from about 44 to 83 percent, preferably from about 50 to 70 percent, by weight cellulose ester solvent. 4

The delustrant mixture is ground or milled in a conventional manner to form a master batch dispersion. The dispersion is then mixed with the preformed polyacrylonitrile spinning solution in an amount such that the spinning solution contains from about 0.05 to 5.0 percent, based on the weight of the solution of the dispersion. Alternatively, the dispersion may be incorporated into the spinning solution by first mixing the dispersion with the acrylonitrile polymer solvent, then adding acrylonitrile polymer powder. After incorporating the delustrant dispersion into the spinning solution, the mixture is stabilized against flocculation, by mixing in a suitable container, such as by tumbling in a stainless steel bomb for from about 1 to 5 hours. The mixture is preferably simultaneously heated while mixing.

The present invention requires that a cellulose ester solution be utilized for dispersing the pigment prior to addition to the acrylonitrile polymeric spinning solution. Although acetone is the preferred solvent, any aliphatic ketone having from 1 to 5 carbon atoms may be used alone, or mixed with up to 20 weight percent water. Other solvents such as methylene chloride, methyl acetate, acetic acid, ethylene formal, cresol, benzyl alcohol or dioxane may be utilized. When solutions of acrylonitrile utilizing such solvents as N,N-dimethyl formamide, dimethyl sulfoxide, ethylene carbonate, propylene carbonate or dimethyl acetamide are used to disperse TiO flocculation or clustering results, particularly when subsequently combined with the polyacrylonitrile spinning solution which utilizes the noted low boiling solvent system.

As referred to herein, acrylonitrile polymers are those containing at least 85 percent acrylonitrile polymers and preferably those containing at least percent acryonitrile by weight. These polymers can be acrylonitrile homopolymers as well as copolymers, terpolymers, multipolymers and the like wherein up to about percent, preferably up to 10 percent of the polymer is another ethylenically unsaturated compound copolymerizable with the acrylonitrile. Such materials can be monomers or polymers which are copolymerizable with acrylonitrile and added to modify and/or enhance certain characteristics of the acrylic polymer. Often, the material copolymerizable with the acrylonitrile contains a chemical group which increases the acid or dyeability of the resulting polymer. Such dye enhancing compounds normally contain a sulfur or phosphorous group in the ethylenically unsaturated chemical entity copolymerizable with the acrylonitrile. Typically, such sulfuror phosphorus-containing compounds are added in an amount of about 0.1 up to about 5 percent by weight of the total polymer composition while the other modifying substance, if any, is added in an amount of up to about 14.9 percent. Typical ethylenically unsaturated monomers copolymerizable with acrylonitrile are methyl acrylate, vinyl acetate, vinylidene chloride, methyl methacrylate, methallyl alcohol, vinylidene cyanide, styrene sulfonic acid materials, sodium methallyl sulfonate, mixtures and partial polymers thereof and the like as are well known to those skilled in the art. The polymers are polymerized by conventional methods such as solution or suspension polymerizations, as well known in the art.

The degree to which the polymer is polymerized is dependent on the end use for which the polymer is intended. Thus, for spinning acrylic fibers, the polymer is preferably polymerized to an intrinsic viscosity of about 0.9 to 2.0 or more, and more preferably about 1.2 to 1.8 (I.V. in a 0.1% solution of the polymer in N,N-dirnethylformamide at 25 degrees centigrade). Of course, higher I.V.s can be used but they result in higher viscosities for given solvent concentrations. For films, molded products, extruded non-fiber products and the like, different I.V.s may be more desirable.

In the solution spinning of fibers, it is preferable to use a high solids concentration in the spinning solution. With the preferred solvent system, such high solid concentrations are readily obtained using the acrylic polymers having I.V.s in the normal range used for acrylic fiber spinning, that is, about 1.2 to 1.8. In particular, solutions of a solids content of about 30 to 70 percent by weight are obtained. The more preferred spinning solutions are obtained in the solid range of about 30 to 50 percent with polymers having I.Vs of about 1.2 to 1.8 or more. With lower I.V. polymers, such as about 0.9 to 1.2, higher solids contents up to about 70 percent or more can be used.

The spinning solutions are formed by mixing the desired solid amount of acrylonitrile polymer with acetonitrile by itself or with Water in an amount up to about 50 Weight percent of the total solvent portion. While a water addition need not be used, it has been found that the addition of water, particularly in the range of about 18 to 27 percent by weight of the acetonitrile solvent portion, lowers the gelation point of the resulting solution, thereby enabling greater flexibility and control of spinning, molding or extruding temperatures.

The acrylic polymer and acetonitrile solvent portion are mixed and cooled to a low temperature, e.g., 0 to -7 degrees centigrade. Mixing is continued, usually for 1 to 7 hours wherein the polymer passes from a solid into a slurry state. The slurry is then heated under superatmospheric pressure to a temperature above the atmospheric boiling point of the solvent and below the polymer degradation temperature (i.e., 80 to 160 degrees centigrade, preferably 90 to 140 degrees centigrade) and held at that temperature for about 1 to 20 hours during which time the slurry passes into a liquid state. Having reached the liquid state, the temperature can then be lowered to about 80 to 85 degrees centigrade Without gelation, if pressure is maintained. The gel temperature on cooling is normally above or near the boiling point of the acetonitrile under process pressure depending on the amount of water present, the polymer I.V., the acrylonitrile content, the solids content and the like.

The superatmospheric pressure utilized to form the solution is preferably at least equal to that required to maintain the acetonitrile solvent portion in substantially the liquid phase. For example, at 130 degrees centigrade and 34 percent solids, the vapor pressure of the dope is approximately 58 p.s.i.g. At degrees centigrade, the vapor pressure is only 20 p.s.i.g.; however, higher pressures such as to 300 p.s.i.g. can conveniently be used if desired.

The invention will be more fully described by reference to the following examples which illustrate certain preferred embodiments of the present invention. Unless otherwise indicated, all temperatures are in degrees centigrade and all parts are by weight.

EXAMPLE I An acrylonitrile copolymer comprising about 94.5 percent acrylonitrile, about 5 percent methylacrylate and about 0.5 percent sodium methallyl sulfonate, polymerized to an intrinsic viscosity of about 1.4 and a molecular weight of about 110,000 was solvated with acetonitrile by placing 36 pounds of the acrylonitrile copolymer into a pressure vessel together with 51.2 pounds of acetonitrile and 12.8 pounds of water. The resulting mixture comprised 36 percent acrylonitrile copolymer solids, 12.8 percent water and 51.2 percent acetonitrile, by Weight (the acetonitrile/water were in a proportion of about 80/20, by weight).

The pressure vessel was sealed and subsequently slowly mixed for eight hours at room temperature, then the temperature was raised slowly to degrees centigrade, at which point the material in the vessel changed from a slurry to a gel-like phase into a homogeneous fluid solution (dope). The mixture was then mixed for about 18 hours more at 110 degrees centigrade while maintaining a pressure of about 50 p.s.i.g., creating a dope viscosity of about 100 poises, at the noted temperature.

A cellulose acetate solution comprising about 6.8 percent by weight cellulose acetate and 93.2 percent by weight acetone was prepared in a conventional manner. Anatase TiO, was added to the cellulose acetate solution in an amount such that the mixture contained about 32.7 percent by weight TiO 4.6 percent by weight cellulose acetate and 62.7 percent by weight acetone. The T i0 pigment was dispersed throughout the cellulose acetate solution by grinding in a ball mill. After ball milling for about 3 hours, about 0.2 percent, by weight based on the weight of the spinning dope of TiO: dispersion, wherein the TiO particle size was less than about 2 microns, was incorporated into the dope by adding the dispersion and spinning dope to a stainless steel bomb, then tumbling for about 3 hours at 110-135 degrees centigrade. The tumbling stabilized the fluid dispersion against flocculation.

The spinning dope prepared by the above procedure was passed to a pressurized dry spinning system. The spinning dope was maintained at a temperature of about degrees centigrade and a pressure of 50 p.s.i.g. Filaments were spun from the solution using a spinneret having micron jet openings of round configuration. The filaments were dry spun at 100 meters per minute into a column maintained at a temperatrue of from about 40 to 60 degrees centigrade. The resulting filaments had a low sheen (i.e., were delustered) and had round, serrated cross sections. The as-spun filaments were subsequently afterdrawn at a draw ratio of about 2: 1.

Four acrylonitrile polymer solvents were evaluated as dispersion media for TiO- Anatase TiO was milled in solutions of acrylonitrile polymer in these solvents. N,N- dimethyl formamide gave a somewhat stable dispersion, whereas dimethyl acetamide, 80/20 ethylene carbonate/ propylene carbonate and dimethyl sulfoxide all gave flocculated dispersions. When the N,N,-dimethyl formamide dispersion of TiO was mixed with the acrylonitrile polymer spinning solution, a flocculated state resulted that persisted into yarn. In all of the above runs, TiO was added at a level of 0.25 percent, based on the weight of acrylonitrile polymer. Table I below lists the dispersion formulations tested.

TABLE I.DISPERSIONS IN ROOM TEMPERATURE SOLU- TIONS OF ACRYLONITRILE COPOLYMER The method of Example I was repeated, except that the TiO dispersion in the cellulose acetate solution was added to the acetonitrile/water solvent together with the acrylonitrile copolymer, prior to solvation of the acrylonitrile copolymer with the acetonitrile/water solvent. The mixture was then tumbled in a stainless steel bomb for about 3 hours at 110 to 135 degrees centigrade. The dope was then spun as in Example I. The spun filaments were delustered, as in Example I.

EXAMPLE HI The method of Example I was repeated, except that the cellulose acetate solution initially prepared contained about 14.3 percent by weight cellulose acetate dissolved in acetone. The final Ti0 dispersion contained about 35 percent by weight TiO percent by weight cellulose acetate, and about 60 percent by weight acetone. This dispersion was added to the acrylonitrile polymer spinning solution as in Example H and a fiber spun which contained about 0.20 percent by weight, based on the weight of acrylonitrile copolymer, of TiO The spun filaments were delustered, as in Example I.

EXAMPLE IV The method of Example I was repeated, except that the initial cellulose acetate solution prepared contained about 6.8 percent by weight cellulose acetate in acetone. TiO was added to this solution such that a mixture containing about 32.7 percent by weight cellulose acetate and 62.7 percent by weight acetone resulted. The TiO was dispersed throughout the cellulose acetate solution, as in Example I, and added to the acrylonitrile polymeric spinning solution, as in Example I. Filaments were spun which contained about 0.25 percent by weight, based on the weight of acrylonitrile copolymer, of TiO The spun filaments weredelustered as in Example I.

Similar results are obtained using as a dispersant a cellulose ester in other solvents such as methylene chloride/methanol, methylene chloride/ethanol, methylethyl ketone, methyl acetate, acetic acid, ethylene formal, cresol, benzyl alcohol or dioxane.

While there have been described various embodiments of the present invention, the methods and products described herein are not intended to be understood as limiting the scope of the invention, as it is realized that changes therein are possible. It is intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results and substantially the same or equivalent manner. It is intended to cover the invention broadly in whatever form its principles may be utilized, being limited only by the appended claims.

What is claimed is:

1. An acrylonitrile spinning solution consisting essentially of from about 30 to weight percent of an acrylonitrile polymer of at least percent by weight acrylonitrile and up to 15 percent by weight of another ethylenically unsaturated compound copolymerizable therewith, selected from the group consisting of methyl acrylate, vinyl acetate, vinylidene chloride, methyl methacrylate, methallyl alcohol, vinylidene cyanide, and sodium methallyl sulfonate and mixtures and partial polymers thereof in a solvent, therefor, and from about 0.05 to 5 weight percent of a delustrant dispersion in a solution of a cellulose ester in a solvent which is a non-solvent for high acrylonitrile polymers, selected from the group consisting of aliphatic ketones having from 1 to 5 carbon atoms, methylene chloride, methyl acetate, acetic acid, ethylene formal, cresol, benzyl alcohol, and dioxane mixed with up to 20 weight percent water said dispersion consisting essentially of from about 15 to 45 weight percent particulate delustrant pigment, from about 1 to 17 weight percent of a cellulose ester and from about 44 to 83 weight percent cellulose ester solvent.

2. The composition of claim 1 wherein the particulate delustrant consists essentially of pigmentary TiO 3. The composition of claim 1 wherein the cellulose ester is cellulose acetate.

4. The composition of claim 1 wherein the cellulose ester solvent is acetone.

5. The composition of claim 1 wherein the solvent for the acrylonitrile polymer consists essentially of acetonitrile and up to about 50 weight percent water.

6. The composition of claim 1 wherein the particulate delustrant is TiO 7. The composition of claim 6 wherein the TiO;, has a particle size of less than about 10 microns.

8. The composition of claim 1, wherein the cellulose ester solution consists essentially of from about 25 to 35 weight percent particulate delustrant, from about 3 to 15 weight percent cellulose ester and from about 50 to 70 weight percent celluloseester solvent.

References Cited UNITED STATES PATENTS 2,819,173 1/ 1958 Dithmar 106-166 2,990,291 6/ 1961 Bartholomay 106192 3,076,771 2/1963 Coover 26017 R 3,145,186 8/1964 Lowes 26017 R 3,268,490 8/1966 Sunden et al. 26085.5 S X WILLIAM H. SHORT, Primary Examiner L. M. PHYNES, Assistant Examiner U.S. Cl. X.R.

26029.1, 41 B, 79.3, 85.5 S, 88.7 B 

